Creating a believable character is harder than it sounds. Unlike a play, a novel doesn’t have a list of the characters the reader will eventually encounter. The novelist introduces them throughout the story using a variety of methods to flesh out just who they are. At least that’s an approach I prefer.
A physical description obviously gives the reader an immediate mental picture to associate with a particular character. In addition to a static picture, the description can include idiosyncratic movements and habits, both deliberate and unconscious. While such an approach is certainly effective, an extensive and detailed description for every character as he or she is introduced is tiresome for both the author and the reader. On the other hand, drawing out the description and adding details here and there over too many pages or chapters runs the risk of adding detail that is out of synch with an image already in the reader’s mind. I’ve found that once I have a mental picture of a character it sticks with me throughout the story, unless the author at some point later adds an attribute that is entirely at odds with that picture forcing me to alter my image.
I often choose to dribble out physical characteristics and idiosyncrasies over the course of a scene, revealing much about the character but taking three or four pages to do so rather than one descriptive paragraph for the same purpose. Those pages might contain dialog lending further texture to the character either through the character’s choice of words, or my aural descriptions of the character’s delivery. The character’s body language in reaction to what others say or do is another helpful tool, particularly when establishing the relationship between those conversing. Pauses, facial expressions, head and body movements, involuntary ticks such as coughing, scratching, playing with a pencil, a cigarette, a pair of glasses, and the like all help define a character during a piece of dialog.
Finally, a character’s actions are most crucial for getting to the core of who she is. Is she timid, brave, careless, dismissive, haughty, imperious, cynical, modest, aggressive, treacherous, quick-witted, dull, submissive, or any other of the almost limitless attributes humans display? It is one thing to insist that a character is brave. The reader is stuck with that shallow declaration. It is another to describe an action the reader associates with the character. At that point, the reader gets to decide whether the character is brave or foolish, whether she runs on fierce and admirable instinct or rushes headlong foolishly and lacks sound judgment. The fact is that different readers will judge the same character differently. Insisting that a character is all this and none of that robs the reader of that choice, and, in my view, diminishes the dynamic experience of reading.
In short, there is only so much an author can do, and it is just as true that there is only so much an author should do.